A Text-Book of Inorganic Chemistry #261999

The nineteenth century was an era Of great prosperity for scientific, inquiry. For numerous phenomena explanations have been found which possess a great degree Of probability. Still it cannot be denied that the present theories penetrate only a little into the real essence Of things, and the investigator Very soon stumbles upon questions whose explanation does not at present even seem to be a possibility. The chemical process that goes on when copper — to retain our former example — is heated in the air is well known. However, the deeper question, why the action takes place just SO and not otherwise, or why the resulting powder is black, still awaits a satisfactory answer.